1. Field of the Invention
This invention relates to frequency or band elimination filters commonly called notch filters, and particularly to a filter of this class having improved rejection characteristics.
2. General Description of the Prior Art
The principal type of filter used as a trap or band elimination filter is a bridged-T filter consisting of two series capacitors bridged by a resistor at the top portion of the T configuration and an inductor connected between the capacitors and a common terminal. A difficulty with this filter is that for some applications the slope of the rejection characteristic on each side of the design frequency is insufficient, that is, the cutoff is not sharp enough. While improved sharpness of cutoff can be achieved utilizing crystals, the problem with the crystal filters is that spurious responses are often passed which are sufficiently close to the notch frequency to be objectionable.
Accordingly, it is an object of this invention to provide a new and improved notch filter which approximates the steepness of a crystal filter without the problem of spurious responses.